Commercially available independent flow and pressure control systems for dispensing agrochemicals onto fields exist and are well documented in the prior art. These systems utilize a plurality of solenoid actuated valves that pulse according to a on/off ratio which determines the flow from the group of nozzles at any given pressure. Therefore, the pressure of the system can be controlled for such parameters as droplet size, system flow capacity, stream dynamics, injection penetration, etc., while the flow of the system is independently controlled for such parameters as application rate (gallons/acre). These systems are commercially available for agricultural liquid applications of pest control sprays and crop nutrient systems. All nozzles within these existing commercial systems pulse together at the same rate.
Such systems for dispensing agrochemicals as described above are described, for instance, in U.S. Pat. No. 5,967,066 and in U.S. Pat. No. 7,502,665, which are incorporated herein by reference. The systems described in the above patents include a liquid reservoir for containing an agrochemical placed in communication with a plurality of valves positioned on a boom. In the '665 patent, a networked delivery system is described that includes a communication network to establish operative communication between individual device nodes and a central operator interface. In the '665 patent, for instance, a plurality of vibration sensors can be located adjacent to respective nozzles or valves that indicate to the operator whether the valves are operating properly.
The systems described in the '066 patent and in the '665 patent represent great advances in the art. Although the systems described in the above patents, however, suggest controlling the application rate of the agrochemical based on individual solenoid valves, various improvements in the art are still needed.
In particular, a need currently exists for an improved system and method for controlling individual valves or groups of valves for varying application rates. A need also particularly exists for such a control system that is capable of being retrofitted onto existing systems.